Lashed-lug boats are ancient boat-building techniques of the Austronesian peoples. It is characterized by the use of raised lugs (also called "cleats") on the inner face of hull planks. These lugs have holes drilled in them so that other hull components such as ribs, thwarts or other structural components can be tied to them with natural fiber ropes (hence "lashed"). This allows a structure to be put together without any metal fastenings. The planks are further stitched together edge-to-edge by sewing or using dowels ("treenails") unto a dugout keel and the solid carved wood pieces that form the caps for the prow and stern. Characteristically, the shell of the boat is created first, prior to being lashed unto ribs. The seams between planks are also sealed with absorbent tapa bark and fiber that expands when wet or caulked with resin-based preparations.

Lashed-lug construction has been used on a wide size range of vessels, from small craft, such as logboats that have had planks added to their sides to increase their freeboard, to large plank-built ships. It is found in traditional boats of Maritime Southeast Asia, Melanesia, Madagascar, Micronesia, and Polynesia. It forms part of the maritime technology used by Austronesian peoples in their spread throughout the islands of the Indo-Pacific starting at 3000 to 1500 BCE. The oldest recovered remains of ships of lashed-lug construction is the Pontian boat of Malaysia dated to at around c.260–430 CE.

The lashed-lug technique of Austronesians is considered to be very similar to that found in archaeological remains of some northern-European boats. This is considered to be a case of independent invention of one of a limited number of solutions to the same boat-building problem.

The lashed-lug technique remains remarkably homogeneous throughout the entirety of the Austronesian range. The keel and the base of the hull is a simple dugout canoe. Planks are then added gradually to the keel, either by sewing fiber ropes through drilled holes or through the use of internal dowels ("treenails") on the plank edges. Unlike carvel construction and in common with many early boat building methods, the shell of the boat is created first, prior to being fastened to the ribs. The seams between planks are also sealed with absorbent tapa bark and fiber that expands when wet or caulked with resin-based preparations.

The most distinctive aspect of lashed-lug boats are the lugs (also called "cleats" by some authors). These are a series of carved protrusions with holes bored into them on the inside surfaces of the planks which are then lashed tightly together with the lugs on the adjacent planks and to ribs using plaited fiber (usually rattan, coir, and other palm fibers).

The seams of the planks were commonly caulked with resin-based pastes made from various plants as well as tapa bark and fibers which would expand when wet, further tightening joints and making the hull watertight. The ends of the boat are capped with single pieces of carved Y-shaped wooden blocks or posts which are attached to the planks in the same way.

Once the shell of the boat is completed, the ribs are then built and lashed to the lugs to further strengthen the structure of the ship, while still retaining the inherent flexibility of the outer hull. The outriggers, when present, are attached with similar lashings to the main hull.

The smallest Austronesian boat (excluding rafts and dugout canoes) characteristically have five parts all put together using the lashed-lug technique. These consist of the dugout keel, two planks that form the strakes, and the end caps for the prow and the stern. Larger ships usually differed in the number of planks used for the strakes, but the construction techniques remain the same.